Mercury arc rectifier construction



Nov. 28, 1933. A' ATHERTQN 1,936,781

MERCURY ARC RECTIFIER CONSTRUCTION Filed Sept. 2, 1931 2 Sheets-$heet 1WITNESSES: INVENTOR E14 Alfred L, A f/verzo/v BY In. J 6%. MW

ATTORNEY Nov. 28, 1933. ATHERTON 1,936,781

MERCURY ARC RECTIFIER CONSTRUCTION Filed Sept. 2, 1931 2 Sheets-Sheet 2I 1 I l i 4 i l WITNESSES: NVENTOR AZ/red L. Aziverzon. a /Z j WATTORNEY Patented Nov. 28, I933 UNETEE STATES MERGUR'IL ARE BEQTIFHERCONSTR Alfred Wes ting Parser v OFFICE UCTION Atherten, Verona, Pa,assignor to reuse Electric a Manufacturing. Com- My invention relates toa mercury arc rectifier and particularly to a metal-tank rectifier ofsmall size and high efficiency and capacit The metal-tank mercury-arcrectifiers constructed prior to my invention have been provided with alarge central condensing chamber surrounded by an anode-chamber, and amercury cathode, usually centrally located, coo, erated with a pluralityof anodes. When high currents are rectified by these prior devices agreat quantity of mercury vapor is given off by the cathode and mustnecessarily be condensed in order to keep the vapor pressure in therectifier at the proper value.

In order to secure the necessary condensing area the central coolers orcondensing chambers have been made of large size which in turn haspushed the anodes to a great distance from the cathode and increasedthelength of the rectifying arcs. 7

This construction has given rise to tanks of enormous size in which thearc drop is of the ord r of 20 or 40 volts, with a consequentenergy-loss of huge proportions. Since this energy appeared mostly asheat in a substantially complete vacuum, the Working parts werenecessarily at high temperature.

The introduction of these high temperatures to a safe working order hasintroduced still further losses.

Apparently this form of construction was the result of a mistaken ideaconcerning the nature of the vapor-flow from the cathode. It has longbeen known that the quantity of vapor flowing from the cathode to theanodes exerted a material influence on the operating characteristics ofthe rectifier.

It has been heretofore believed that the mercury-vapor leaving thecathode acted very much like a jet and flowed substantially in astraight line. Consequently the centralc ndensing ch 2 her in directcommunication With the cathode was believed to be the best method ofeliminating vapor-flow into the anode spaces. However, it

was suspected that a certain amount of mercury-. In order sufiicientcooling to reduce causing difficultie tion, the mercury vapor, insteadof flowing as a jet-develops a complete randomness of directionimmediately after it is released from the cathode, or if an arc-guard isused, immediately beyond the termination of the arc-guard, so that thevapor behaves as any other high-pressure gas released in a low-pressurearea and moves outin all directions.

The rectifier of my invention takes account of the nature of vapor-flowfrom the cathode, and instead of trying to confine the vapor to acentral condenser and excluding it from a large anodearea, I haveclustered the anodes in closely spaced relation, both with respect toeach other and with respect to the cathode, and I have excluded thevapor from this relatively small area, While permitting it to flowfreely into the remainder of the tank.

The anodes are placed as close togetherias is convenient mechanically,and they are enclosed in a common shield having openings adjacent to theanode faces for the passage of the arcs, thus eliminating the customaryconfining shields and grids, and leaving the arcs substantiallyunconfined, while materially reducing the arc-length. The short,substantially unimpeded arc reduces the arc-drop; from 40 volts of theconventional rectifier to approximately 12 volts. 1

However, I still found that sufiicient mercuryvapor entered theanode-chamber to have a deleterious influence on stability. In order toprevent I the vapor from the cathode fromentering the anode-space, Ihave provided-an auxiliary source of mercury vapor from which vapor ofsufficient pressure and-quantity to counteractthe vaporflOW from thecathode is conducted to the anodechamber. This auxiliary vapor-flowprevents the highly ionized vapor from the cathode from coming intodirect contact with the anodes and materially reduces the probability ofback-fire in the rectifier.

I have found that there are accumulations of non-condensing gases atvarious places in the rectifier and that these accumulations depend onthe flow of the nercury-vapor from the cathode to the condensingsurfaces. Apparently, when the mercury-vapor flows into a closed pocket,the Walls of which are condensing surfaces, the foreign gas is carriedalong and retained in the pocket by the continued flow of vapor. Anyinstability thereupon permits this foreign gas to flow out,

troduced by'the presence of the foreign gas itself.

It is quite probable that unanodes. tensions 16 on the main shield 12,extending be- The accumulation of foreign gas will continue until it issufiicient to have a pronounced effect on the now of the mercury-vapor,at which time the vapor is prevented from reaching some of thecondensing surface. The vapor is, therefore, deflected and as a resultthe accumulated foreign gas can flow out of the pocket and, particularlyif in the vicinity of the anodes, may cause backfire in the rectifier.

Since it is apparent that there is always some foreign gas to contendwith, this problem becomes one of major importance. In fact, it may bethe greatest source of difficulty with rectifiers.

In the rectifier of my invention, this source of trouble is removed, asthe auxiliary vapor-stream is supplied from a portion of the rectifierfrom which impurities and foreign gas are excluded. The auxiliaryVapor-stream prevents gas from other parts of the rectifier fromentering the anode-chamber, while the fiow of gas around the anodesproduces a pumping action to remove any gas generated at the anodes andto carry it to the condensing chamber from which it is most easilypumped by any suitable means. I

By the use of my clustered anodes, together with short are lengths, therectifier, according to my construction, is of much smaller size thanrectifiers of similar capacity, according to conventional designs.

Also, by the shortening of the arc-length and the elimination of therestricting shields and the control-grids, made possible by the use ofthe auxiliary vapor blast, the power-loss in the arcs has beenmaterially reduced, so that the efficiency of the rectifier has beenmaterially increased. Less energy-loss results in less cooling-surface,and thus still smaller and moreeificient rectifiers are produced.

Other objects and advantages of my invention will be apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawings, in which,

Figure 1 is a sectional elevation of a preferred embodiment of myinvention,

Fig, 2 is a sectional plan view along line II-II of Fig. 1 showing theinterior arrangement,

Fig. 3 is a sectional elevation of a modification,

Fig. 4 shows a further modification, and

Fig. 5 is a cross-sectional view on line V-V of Fig. 4.

In the embodiment of my invention, according to Figs. 1 and 2, therectifier comprises a watercooled metal tank 1 ofsubstantiallycylindrical construction, having an insulated cathode plate2 secured thereto, the cathode plate carrying an annular cathode pool 5and a central auxiliary pool 6 fed from the cathode pool by a duct 7,but shielded from the rectifying arc, so as to be distinct and separatefrom the cathode 5.

A plurality of anodes 10 are nested as closely together as ismechanically convenient and are surrounded by a single shield 12 of asize suiiicient to enclose the anode space. The shield 12 is provided,near its bottom and adjacent to the anode faces, with openings 14 forthe rectifying arcs.

It is characteristic of vapor-electric devices that where objects athigh differences of potential are separated by very short distances thepotential gradient is such that there is little likelihood of breakdown,and since the shields are at substantially cathode potential it isdesirable that the shields approach closely to the bodies of theTherefore I provide partitions or exvide an anode-chamber 22, leavingonly the radial openings 14 for the rectifying arcs. However, sincethese radial openings 14 are in proximity to the anode surfaces, themain portion of the rectifying arcs are outside of the anode chamber 22and are substantially unconfined.

Surrounding the anode-chamber and occupying the remainder of the tank isa condensing chamber 25 directly open to the vapor from the cathode 5and provided with one or more ring coolers 26.

The auxiliary mercury pool 6 is provided with a suitable heater 30 ofany desired type for producing mercury vapor. Immediately above thisauxiliary pool is a conduit or chimney 31 for conducting the mercuryvapor to the anode chamber 22, preferably to the top wall 18 of theanode chamber 22, which is depressed in a substantially conical form inproximity to the chimney 31. This conical depression acts as a spreaderfor directing the mercury vapor from the chimney 31 toward the anodes10, so that the auxiliary vaporflow passes around the anodes, and sweepsover the surfaces thereof in the direction of the radial arc passages,so that the direction of the auxiliary vapor-flow in the arc passages isopposite In addition to the pumping action of the auxiliary vapor, thecounter-flow or counter-pressure in the anode chamber produces aconstant fiow or condition of vapor in the vicinity of the anodes, asdistinguished from the gusty, turbulent gasfiow believed to exist inprevious rectifiers. probably follows from the fact that the vapor isproduced steadily and because, as a result of the shape of the stack 31and the cooperating baffle 18, the auxiliary vapor flows instream-lines, while in the previous devices the vapor was releasedprincipally in the vicinity of the cathode spot or spots with resultantswirls and eddies.

The cathode spot on an annular cathode appears reluctant to move awayfrom the keepelive, resulting in unequal arc lengths from the variousanodes and unequal arc losses, if only one keepalive is used.

The rectifier of my invention is provided with a plurality ofkeep-alives 35 so spaced that a cathode spot is always maintainedadjacent to each of the anodes or group of anodes, so that the arcs areof approximately the'sarne length. I have provided radial shields 36 forpartitioning the condensing chamber 25 into a plurality of chamberscorresponding to the number of keepbeen reconstructed to bettercooperate with the smaller annular cathode.

Because of the absence of cooling surfaces around the auxiliary pool,the mercury therein is normally at about the same temperature as themercury in the cathode, so that only a comparatively small amount ofheat is needed, in the heater 3-9, to produce sufficient auxiliary vaporto counteract the tendency of the cathode-vapor to enter theanode-chamber.

In the modification according to Figs. l and 5, the anodes 16 have beenclustered adjacent to the sides or" a substantially rectangular tank,the clustered anodes being provided with a common shield to provideanode chambers at the sides of the tank, and a longitudinally extendingcentrally located cooling chamber. The anodes cooperate with aconventional centrally located cathode 42.

Each of the anode-chambers is provided with an auxiliary mercury poolhaving a chimney e for supplying auxiliary vapor to the anode spaces.

The quantity of ionized vapor given off the cathode during operation isdirectly de- Consequently the vapor-pressure in the rectifier increaseswith the load. The increased vapor-pressure tends to force ionized vaporinto the anode-spaces so that it is desirable to vary the auxiliaryvapor pressure to counteract the increased-vapor pressure from thecathode. This may be accomplished by varying the input into the heatersin response to load-variations. If direct current is use in the heatersthey may be connected in series with the output of the rectifier, or if1 alternating current is supplied to the heaters the same response toload conditions may be secured by supplying the current by currenttransformers in the supply-leads of the rectifier. By the variation ofthe capacity of t e heaters in response to load conditions, the optimumquantity of auxiliary vapor may be supplied at all times.

While I have shown and described three embodiments of my invention, itis apparent that changes and modifications can be made therein withoutdeparting from the spirit and scope of my invention. I desire,therefore, that only such limitations shall be imposed as are embodiedin the accompanying claims or as may be necessitated by the prior art.

I claim as my invention:

1. An evacuated metal-tank mercury-arc rectifier comprising a mercurycathode, said tank including a lar e evacuated cooling chamber adjacentto said cathode, a plurality of anodes so positioned that the are froman anode to the cathode passes through a portion of the cooling chamber,a pool of mercury other than the cathode, and means for producing astream of mercury-vapor from said pool for counteracting thevapor-stream from the cathode.

2. An evacuated metal-tank mercury-arc rectifier comprising a mercurycathode, said tank including a large evacuated cooling chamber adjacentto said cathode, a plurality of anodes so positioned thatv the are froman anode to the cathode passesthrough'the cooling chamber, a pool ofmercury other than the cathode, a heating element for said pool andmeans fordirect ing a stream of mercury-vapor from said pool through theanode-space, the quantity and velocity of the vapor-stream beingsuificient to counteract the tendency of the cathode-vapor to enter theanode-space.

A vapor-electric device comprising a metal tank, a plurality ofcloselyspaced anodes in said tank, a mercury cathode in said tank, acondensing chamber adjacent to said cathode, baiiles for directingmercury-vapor away from said anodes into said condensingchainber, a bodyof niecury other than said cathode in the' tank, a heater for said bodyof mercury, and means for conducting vapor from said body of mercuryinto the vicinity of the anodes and thence in the arc-path.

4. In a vapor-electric device, a mercury cathode, a condensing chamber,an anode chamber, a plurality of anodes in said chamber, the anodechamber being open to the cathode, a pool of mercury separate'from saidcathode, a heating element for said mercury pool, and a conduit forconducting mercury vapor from the pool to the anode chamber.

5. A mercury-arc rectifier comprising a container, an annular cathodepool therein, a plurality of anodes nested in said container, a shieldaround said anodes to provide a small anode chamber, a comparativelylarge condensing chamber surrounding said anode chamber, a plurality ofshields for dividing said anode chamber and said condensing chamber intoa plurality of sections, and a keep-alive in each section.

6. A mercury-arc rectifier comprising a metal tank, an annular cathodepool therein, a plurality of anodes clustered in said tank, a shieldaround said anodes to provide a small anode chamber, a comparativelylarge condensing chamber surrounding said anode chamber, a plurality ofradial shields for dividing said condensing chamber into aplurality ofsegmental sections,

a keep-alive in each section, a centrally disposed auxiliary mercurypool shielded from the arc, a heating element for said pool, and achimney for conducting mercury vapor from said pool to said anodechamber. V

7. A mercury-arc rectifier comprising a pluralityof anodes, a shieldproviding a partially closed anode chamber, a condensing chamber, avaporizable cathode open to said condensing chamber and an auxiliarysource of .mercury vapor for preventing vapor from said cathode fromentering the anode chamber.

8. A mercury-arc rectifier comprising a plurality of anodes, a shieldproviding a partially closed anode chamber, a condensing chamber, avaporizable cathode open to said condensing chamber, an auxiliary sourceof mercury vapor for preventing vapor from said cathode from enteringthe anode chamber, a chimney for conducting vapor from the auxiliarysource to the anode chamber, a top shield in the anode chamber shaped tospread the vapor flow evenly the anode and means comprising a source ofauxiliary vapor for deflecting the cathode vapor 'from the common anodeshield.

10. A mercury-arc rectifier comprising a container, a mercury cathodetherein, a plurality of anodes, an anode chamber substantially enclosingsaid anodes, an opening in said chamber for the passage of therectifying arc, a body of mercury other than the cathode, vaporizingmeans for producing mercury vapor from said body of mercury, said meansbeing responsive to load current, and means for conducting the mercuryvapor into the anode chamber.

11. A vapor-electric device comprising a vaporizable cathode, aplurality of anodes cooperating with the cathode to produce arc streamsof ionized mercury vapor, a condensing chamber separated from saidanodes, a source of auxiliary mercury vapor and means for causing saidauxiliary vapor to sweep across the surface of said anodes.

12. A mercury-arc rectifier comprising a mercury cathode, a condensingchamber open to said cathode, an anode chamber, a plurality of anodestherein, a source of mercury vapor other than the cathode and means forcausing a blast of mercury vapor from said source to flow through.

